1. Field of the Invention
The present invention relates to a method for preparing amino acid esters using sulfuric acid as the catalyst.
2. Discussion of the Background
L-phenylalanine methyl ester is an important intermediate for preparing .alpha.-L-aspartyl-L-phenylalanine methyl ester which has been in the spotlight lately as a low-calorie sweetener. A method of esterifying amino acids with sulfuric acid as the catalyst is known which involves heating an amino acid in an alcohol in the presence of sulfuric acid. This process is described in U.S. Pat. No. 4,680,403. However, it has a serious drawback in that the yield is low. The purpose of the present invention is to provide a method for preparing amino acids in higher yield.